Photonic crystals are spatially periodic structures having useful electromagnetic wave properties, such as photonic bandgaps. In principle, the spatial periodicity of a photonic crystal can be in one, two, or three dimensions. There is especially high interest in developing technology of artificial photonic crystals that are useful in new and improved functional photonic devices, especially for the infrared and visible-light portions of the electromagnetic spectrum. Functional devices using photonic crystals, such as selective reflectors, filters, optical couplers, resonant cavities, delay lines, and waveguides have been proposed and/or fabricated.
A photonic crystal may be provided on a substrate by forming the photonic crystal in place or by placing the photonic crystal on a substrate. Silicon is a convenient substrate on which to build a photonic crystal, especially because of its compatibility with semiconductor-type processing methods and processing equipment. For some applications of photonic crystals, conductive connections connect to the photonic crystal and may also be carried by the substrate. Photonic crystals can emit or direct light into undesired directions and such light may be lost. While some methods for making photonic crystal devices are known, improved methods for mass-production fabrication of photonic crystal devices are needed.